This invention relates generally to filters and more particularly has reference to a filter for use inside hot air nozzles in a paint drying oven.
Examples of pertinent patents are U.S. Pat. Nos. 2,445,074; 1,211,325; 3,808,703; 3,877,107 and 2,448,834.
U.S. Pat. No. 2,445,074 discloses a spray booth used to paint a vehicle and quickly dry the paint by passing air through the booth. The air is passed through filter-containing doors in the booth to prevent blemishes on the newly painted car.
U.S. Pat. No. 1,211,325 shows a drying room with means for removing dust from air passed through the room. The air is cleaned by spraying it and then passing it through screen filters before it enters the room.
U.S. Pat. Nos. 3,808,703; 3,887,107 and 2,448,834 disclose automobile drying apparatus used for drying a car after a car wash.
None of the patents discloses a filter in a nozzle of a hot air blowing apparatus.
In conventional automobile paint drying ovens, hot air at approximately 500.degree. is blown in a downward or sideways direction through nozzles to aid in drying a freshly painted car or vehicle. Known drying booths have approximately 500 nozzles. Each nozzle is about 6 inches in length and extends vertically downwardly from upper ceiling ductwork or inwardly from wall ductwork. The inlet of each nozzle is about 4 inches in diameter, tapering down to approximately 21/4 inches in diameter where the air actually leaves the nozzle and enters the oven environment. Each nozzle handles approximately 110 CFM per 21/4 inch opening at a pressure of approximately 1/2 inch. Hot air is expelled from each nozzle at a rate of approximately 3985 feet per minute.
A difficulty encountered in such drying booths is that the air tends to pick up any old rust and scale which accumulates on the inside of the ductwork. As the air is forced outward, small chips break loose and are carried by the air and become embedded in the newly painted vehicle. The vehicles then have to be resanded, repainted and redried, and it is very difficult to maintain quality control during those steps.
Attempts have been made to overcome the problem by attaching external filters on the exhaust side of the nozzle or by placing filters in the nozzle feed line. Neither attempt has proved satisfactory.
The nozzles are usually positioned on the feed line on 7 inch center holes. That close spacing between nozzles limits the size of the filter which can be used. External filters are generally large and require space consuming attachments, making them unsatisfactory for use with closely spaced nozzles and for access by maintenance people.
External filters also have an adverse effect on the air directional function of the nozzles.
Filters placed in the feed line have the disadvantage of being difficult to install and remove.
Yet another problem with the prior art filters is their inability to filter particles in the micron range without adversely restricting air flow through the nozzles.